As a stator core of a rotating electrical machine such as an AC generator for vehicles, a helical fixed iron core (helically stacked core) is used.
The helically stacked core (hereinafter, simplified to helical core) is constituted by punching one side in a width direction of a strip of steel sheet in a rectangular shape at a fixed interval to form a core sheet with a plurality of slots and teeth, winding the slotted core sheet spirally so that the core sheet is stacked, and joining between the stacked core sheets.
When winding the helical core spirally and stacking it into the cylindrical (toric) shape, another side of the core sheet is rolled.
For this reason, the core sheet stacked spirally has the side (core-back part) whose thickness is thinner than the side where the slots and teeth are formed.
As a result, gaps are produced between the stacked core sheets on an outer circumferential side (core-back part) of the cylindrical helical core.
Moreover, when forming the cylindrical helical core by rolling the core-back part of the core sheet, some misalignment occurs in an outer circumference and an inner circumference of the helical core between each layer, and dispersion in a radius from a central axis occurs.
For this reason, a finishing process that reforms the misalignment and corrects the inner and outer circumferential surfaces to predetermined sizes is needed as a following process to the above-mentioned winding process.
A conventional manufacturing method of a helical core is explained with a flow chart shown in FIG. 2A.    A) Pressing process: forms a core sheet that has slots punched out on one side of a strip of steel sheet at a fixed interval to form teeth between the slots, and core-back parts on another side of the steel sheet.    B) Winding process: rolls a thickness direction of the core-back parts of the core sheet into a tapered shape by using such as a roller, and forms a stacked core by winding spirally and stacking cylindrically the core sheet so that the teeth are positioned in an inner diameter side of the stacked core.    C) Joining (welding) process: joins between each layer of the stacked core by welding etc.    D) Finishing process: consists of an ironing process that corrects inner and outer circumferential surfaces of the stacked core to a predetermined size and a deburring process that removes burr produced by the ironing process.    E) Cleaning process: removes oil etc. applied to processing parts for reducing friction of the ironing process during the finishing process.
As a conventional finishing process, Japanese Patent Application Laid-Open Publication No. 2006-246586 discloses a method of forming inner and outer circumferential surfaces and shapes of slots with high precision by ironing the inner and outer circumferential surfaces while pressing a stacked core.
Moreover, Japanese Patent Application Laid-Open Publication No.2007-135314 discloses a technology that corrects an outer circumferential side perpendicular to a plate surface by disposing a coining punch, which is divided in a plurality of pieces in a circumferential direction, on a perimeter of a stacked core, and coining by pressing the coining punch inside the radial direction.
Furthermore, Japanese Patent Application Laid-Open Publication No.2001-112197 discloses a problem that a stator core deforms when sandwiched by a frame if a gap exists between core sheets in an outer circumferential side of the cylindrically stacked core.
In the method of manufacturing the stator core disclosed in the publication '586, the outer circumferential surface of the stacked core sheet is sheared by moving an outer circumferential surface forming part in a stacking direction as it slides from the outer circumference of the stacked core while moving the stacked core sheet in an inner radial direction, then arrayed.
Thereby, the inner and outer circumferential surfaces can be corrected to predetermined sizes, however, the outer circumferential surface of the stacked core is easily turned over by frictional force and gaps between the core sheets expand partially, thus rain infiltrates inside the stacked core easily.
Moreover, a deburring process that removes burr produced by an ironing process, and a cleaning process that removes oil etc. applied for reducing friction of the ironing process are required, therefore a finishing process consumes man-hours.
On the other hand, an inner circumferential surface formation part for stators, a slot arrow, an end side holding member, etc. applied to the molding device disclosed in '586 are not adopted in a manufacturing method of a stator core disclosed in '314.
Therefore, problems arise easily such as an inner circumferential surface overrun that an inner diameter becomes smaller than a predetermined size, irregular slot sequence in which the slots lose shape, and floating teeth.
A problem arises in '197 that when a steel plate sheet is made thin in the stacked core for reducing iron loss, and the perimeter of the core-back part is thinned by rolling, a thickness in a stacking direction is compressed and a frame is distorted when bound tight with the frame.